The first minor planet to be discovered was Ceres in 1801, the term minor planet has been used since the 19th century to describe these objects.[4] The term planetoid has also been used, especially for larger (planetary) objects such as those the International Astronomical Union (IAU) has called dwarf planets since 2006.[5][6] Historically, the terms asteroid, minor planet, and planetoid have been more or less synonymous.[5][7] This terminology has become more complicated by the discovery of numerous minor planets beyond the orbit of Jupiter, especially trans-Neptunian objects that are generally not considered asteroids.[7] A Minor planet seen releasing gas may be dually classified as a comet.

Objects are called dwarf planets if their self-gravity is sufficient to achieve hydrostatic equilibrium and form an ellipsoidal shape. All other minor planets and comets are called small Solar System bodies,[1] the IAU stated that the term minor planet may still be used, but the term small Solar System body will be preferred.[8] However, for purposes of numbering and naming, the traditional distinction between minor planet and comet is still used.

Hundreds of thousands of minor planets have been discovered within the Solar System and thousands more are discovered each month, the Minor Planet Center has documented over 186 million observations and 754,829 minor planets, of which 513,122 have orbits known well enough to be assigned permanent official numbers.[3][9] Of these, 21,221 have official names,[3] as of 31 January 2018[update], the lowest-numbered unnamed minor planet is (3708) 1974 FV1,[10] and the highest-numbered named minor planet is 495759 Jandesselberger.[11]

There are various broad minor-planet populations:

Asteroids; traditionally, most have been bodies in the inner Solar System.[7]

Near-Earth asteroids, those whose orbits take them inside the orbit of Mars. Further subclassification of these, based on orbital distance, is used:[12]

Apohele asteroids orbit inside of Earth's perihelion distance and thus are contained entirely within the orbit of Earth.

Aten asteroids, those that have semi-major axes of less than Earth's and aphelion (furthest distance from the Sun) greater than 0.983 AU.

Apollo asteroids are those asteroids with a semimajor axis greater than Earth's, while having a perihelion distance of 1.017 AU or less. Like Aten asteroids, Apollo asteroids are Earth-crossers.

Amor asteroids are those near-Earth asteroids that approach the orbit of Earth from beyond, but do not cross it. Amor asteroids are further subdivided into four subgroups, depending on where their semimajor axis falls between Earth's orbit and the asteroid belt;

Earth trojans, asteroids sharing Earth's orbit and gravitationally locked to it. As of 2011, the only one known is 2010 TK7.[13]

Mars trojans, asteroids sharing Mars's orbit and gravitationally locked to it. As of 2007, eight such asteroids are known.[14]

Asteroid belt, whose members follow roughly circular orbits between Mars and Jupiter. These are the original and best-known group of asteroids.

Jupiter trojans, asteroids sharing Jupiter's orbit and gravitationally locked to it. Numerically they are estimated to equal the main-belt asteroids.

Centaurs, bodies in the outer Solar System between Jupiter and Neptune. They have unstable orbits due to the gravitational influence of the giant planets, and therefore must have come from elsewhere, probably outside Neptune.[15]

Neptune trojans, bodies sharing Neptune's orbit and gravitationally locked to it. Although only a handful are known, there is evidence that Neptune trojans are more numerous than either the asteroids in the asteroid belt or the Jupiter trojans.[16]

Out of a total of more than 700,000 discovered minor planets, 66% have been numbered (green) and 34% remain unnumbered (red). Only a small fraction of 20,071 minor planets (3%) have been named (purple).[3][17]

All astronomical bodies in the Solar System need a distinct designation, the naming of minor planets runs through a three-step process. First, a provisional designation is given upon discovery—because the object still may turn out to be a false positive or become lost later on—called a provisionally designated minor planet. After the observation arc is accurate enough to predict its future location, a minor planet is formally designated and receives a number, it is then a numbered minor planet. Finally, in the third step, it may be named by its discoverers. However, only a small fraction of all minor planets have been named, the vast majority is either numbered or has still only a provisional designation. Example of the naming process:

A newly discovered minor planet is given a provisional designation, for example, the provisional designation 2002 AT4 consists of the year of discovery (2002) and an alphanumeric code indicating the half-month of discovery and the sequence within that half-month. Once an asteroid's orbit has been confirmed, it is given a number, and later may also be given a name (e.g. 433 Eros). The formal naming convention uses parentheses around the number, but dropping the parentheses is quite common. Informally, it is common to drop the number altogether, or to drop it after the first mention when a name is repeated in running text.

Minor planets that have been given a number but not a name keep their provisional designation, e.g. (29075) 1950 DA. Because modern discovery techniques are finding vast numbers of new asteroids, they are increasingly being left unnamed, the earliest discovered to be left unnamed was for a long time (3360) 1981 VA, now 3360 Syrinx; as of September 2008, this distinction is held by (3708) 1974 FV1. On rare occasions, a small object's provisional designation may become used as a name in itself: the then unnamed (15760) 1992 QB1 gave its "name" to a group of objects that became known as Classical Kuiper belt objects ("cubewanos") before it was finally named 15760 Albion in January 2018.[18]

Minor planets are awarded an official number once their orbits are confirmed, with the increasing rapidity of discovery, these are now six-figure numbers. The switch from five figures to six figures arrived with the publication of the Minor Planet Circular (MPC) of October 19, 2005, which saw the highest numbered minor planet jump from 99947 to 118161.[3]

The first few asteroids were named after figures from Greek and Roman mythology but as such names started to dwindle the names of famous people, literary characters, discoverer's wives, children, and even television characters were used.

The first asteroid to be given a non-mythological name was 20 Massalia, named after the Greek name for the city of Marseille.[19] The first to be given an entirely non-Classical name was 45 Eugenia, named after Empress Eugénie de Montijo, the wife of Napoleon III, for some time only female (or feminized) names were used; Alexander von Humboldt was the first man to have an asteroid named after him, but his name was feminized to 54 Alexandra. This unspoken tradition lasted until 334 Chicago was named; even then, female names show up in the list for years after.

A well-established rule is that, unlike comets, minor planets may not be named after their discoverer(s). One way to circumvent this rule has been for astronomers to exchange the courtesy of naming their discoveries after each other. An exception to this rule is 96747 Crespodasilva, which was named after its discoverer, Lucy d'Escoffier Crespo da Silva, because she died shortly after the discovery, at age 22.[21][22]

Names were adapted to various languages from the beginning. 1 Ceres, Ceres being its Anglo-Latin name, was actually named Cerere, the Italian form of the name. German, French, Arabic, and Hindi use forms similar to the English, whereas Russian uses a form, Tserera, similar to the Italian; in Greek, the name was translated to Δήμητρα (Demeter), the Greek equivalent of the Roman goddess Ceres. In the early years, before it started causing conflicts, asteroids named after Roman figures were generally translated in Greek; other examples are Ἥρα (Hera) for 3 Juno, Ἑστία (Hestia) for 4 Vesta, Χλωρίς (Chloris) for 8 Flora, and Πίστη (Pistis) for 37 Fides. In Chinese, the names are not given the Chinese forms of the deities they are named after, but rather typically have a syllable or two for the character of the deity or person, followed by 神 'god(dess)' or 女 'woman' if just one syllable, plus 星 'star/planet', so that most asteroid names are written with three Chinese characters, thus Ceres is 谷神星 'grain goddess planet',[23] Pallas is 智神星 'wisdom goddess planet', etc.[citation needed]

Archival data on the physical properties of comets and minor planets are found in the PDS Asteroid/Dust Archive,[25] this includes standard asteroid physical characteristics such as the properties of binary systems, occultation timings and diameters, masses, densities, rotation periods, surface temperatures, albedoes, spin vectors, taxonomy, and absolute magnitudes and slopes. In addition, European Asteroid Research Node (E.A.R.N.), an association of asteroid research groups, maintains a Data Base of Physical and Dynamical Properties of Near Earth Asteroids.[26]

^Objects (generally centaurs) that were originally discovered and classified as minor planets, but later discovered to be comets are listed both as minor planets and comets. Objects that are first discovered as comets are not dually classified.

1.
Planetoid (comics)
–
Planetoid is a comic first released in June 2012 by Image Comics, written and drawn by Ken Garing. In an interview with Comic Book Resources, Garing stated that he spent years working at improvements on Planetoid, then at a convention showed it to Image, the first story arc is a 5-issue mini-series. The story is intended to continue to unfold in further mini-series and it was originally a miniseries available digitally through Graphicly. A second miniseries, Planetoid, Praxis, began in February 2017 and it will be six issues long. Aint It Cool News calls it richly and beautifully illustrated and states that Garing can make beautiful art, multiversity Comics praised Ken Garing’s excellent artistic style and calls him an excellent sequential storyteller

2.
Dwarf planet
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A dwarf planet is a planetary-mass object that is neither a planet nor a natural satellite. The International Astronomical Union currently recognizes five dwarf planets, Ceres, Pluto, Haumea, Makemake, another hundred or so known objects in the Solar System are suspected to be dwarf planets. Individual astronomers recognize several of these, and in August 2011 Mike Brown published a list of 390 candidate objects, Stern states that there are more than a dozen known dwarf planets. Only two of these bodies, Ceres and Pluto, have observed in enough detail to demonstrate that they actually fit the IAUs definition. The IAU accepted Eris as a dwarf planet because it is more massive than Pluto and they subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude brighter than +1 are to be named under the assumption that they are dwarf planets. The classification of bodies in other systems with the characteristics of dwarf planets has not been addressed. Starting in 1801, astronomers discovered Ceres and other bodies between Mars and Jupiter which were for some decades considered to be planets. Between then and around 1851, when the number of planets had reached 23, astronomers started using the asteroid for the smaller bodies. With the discovery of Pluto in 1930, most astronomers considered the Solar System to have nine planets and it was roughly one-twentieth the mass of Mercury, which made Pluto by far the smallest planet. Although it was more than ten times as massive as the largest object in the asteroid belt, Ceres. In the 1990s, astronomers began to find objects in the region of space as Pluto. Many of these shared several of Plutos key orbital characteristics, and Pluto started being seen as the largest member of a new class of objects and this led some astronomers to stop referring to Pluto as a planet. Several terms, including subplanet and planetoid, started to be used for the now known as dwarf planets. By 2005, three trans-Neptunian objects comparable in size to Pluto had been reported and it became clear that either they would also have to be classified as planets, or Pluto would have to be reclassified. Astronomers were also confident that more objects as large as Pluto would be discovered, Eris was discovered in January 2005, it was thought to be slightly larger than Pluto, and some reports informally referred to it as the tenth planet. As a consequence, the became a matter of intense debate during the IAU General Assembly in August 2006. The IAUs initial draft proposal included Charon, Eris, and Ceres in the list of planets, dropping Charon from the list, the new proposal also removed Pluto, Ceres, and Eris, because they have not cleared their orbits. The IAUs final Resolution 5A preserved this three-category system for the bodies orbiting the Sun

3.
Euler diagram
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An Euler diagram is a diagrammatic means of representing sets and their relationships. Typically they involve overlapping shapes, and may be scaled, such that the area of the shape is proportional to the number of elements it contains and they are particularly useful for explaining complex hierarchies and overlapping definitions. They are often confused with the Venn diagrams, unlike Venn diagrams which show all possible relations between different sets, the Euler diagram shows only relevant relationships. The first use of Eulerian circles is commonly attributed to Swiss mathematician Leonhard Euler, in the United States, both Venn and Euler diagrams were incorporated as part of instruction in set theory as part of the new math movement of the 1960s. Since then, they have also adopted by other curriculum fields such as reading as well as organizations. Euler diagrams consist of simple closed shapes in a two dimensional plane that depict a set or category. How or if these shapes overlap demonstrates the relationships between the sets, there are only 3 possible relationships between any 2 sets, completely inclusive, partially inclusive, and exclusive. This is also referred to as containment, overlap or neither or, especially in mathematics, it may be referred to as subset, intersection, curves whose interior zones do not intersect represent disjoint sets. Two curves whose interior zones intersect represent sets that have common elements, a curve that is contained completely within the interior zone of another represents a subset of it. Venn diagrams are a more form of Euler diagrams. A Venn diagram must contain all 2n logically possible zones of overlap between its n curves, representing all combinations of inclusion/exclusion of its constituent sets. Regions not part of the set are indicated by coloring them black, in contrast to Euler diagrams, when the number of sets grows beyond 3 a Venn diagram becomes visually complex, especially compared to the corresponding Euler diagram. The difference between Euler and Venn diagrams can be seen in the following example, the Venn diagram, which uses the same categories of Animal, Mineral, and Four Legs, does not encapsulate these relationships. Traditionally the emptiness of a set in Venn diagrams is depicted by shading in the region, Euler diagrams represent emptiness either by shading or by the absence of a region. Often a set of conditions are imposed, these are topological or geometric constraints imposed on the structure of the diagram. For example, connectedness of zones might be enforced, or concurrency of curves or multiple points might be banned, in the adjacent diagram, examples of small Venn diagrams are transformed into Euler diagrams by sequences of transformations, some of the intermediate diagrams have concurrency of curves. However, this sort of transformation of a Venn diagram with shading into an Euler diagram without shading is not always possible. There are examples of Euler diagrams with 9 sets that are not drawable using simple closed curves without the creation of unwanted zones since they would have to have non-planar dual graphs

4.
Astronomical object
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An astronomical object or celestial object is a naturally occurring physical entity, association, or structure that current astronomy has demonstrated to exist in the observable universe. In astronomy, the object and body are often used interchangeably. Examples for astronomical objects include planetary systems, star clusters, nebulae and galaxies, while asteroids, moons, planets, and stars are astronomical bodies. A comet may be identified as both body and object, It is a body when referring to the nucleus of ice and dust. The universe can be viewed as having a hierarchical structure, at the largest scales, the fundamental component of assembly is the galaxy. Galaxies are organized groups and clusters, often within larger superclusters. Disc galaxies encompass lenticular and spiral galaxies with features, such as spiral arms, at the core, most galaxies have a supermassive black hole, which may result in an active galactic nucleus. Galaxies can also have satellites in the form of dwarf galaxies, the constituents of a galaxy are formed out of gaseous matter that assembles through gravitational self-attraction in a hierarchical manner. At this level, the fundamental components are the stars. The great variety of forms are determined almost entirely by the mass, composition. Stars may be found in systems that orbit about each other in a hierarchical organization. A planetary system and various objects such as asteroids, comets and debris. The various distinctive types of stars are shown by the Hertzsprung–Russell diagram —a plot of stellar luminosity versus surface temperature. Each star follows a track across this diagram. If this track takes the star through a region containing a variable type. An example of this is the instability strip, a region of the H-R diagram that includes Delta Scuti, RR Lyrae, the table below lists the general categories of bodies and objects by their location or structure. International Astronomical Naming Commission List of light sources List of Solar System objects Lists of astronomical objects SkyChart, Sky & Telescope Monthly skymaps for every location on Earth

5.
Orbit
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In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet about a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating path around a body, to a close approximation, planets and satellites follow elliptical orbits, with the central mass being orbited at a focal point of the ellipse, as described by Keplers laws of planetary motion. For ease of calculation, in most situations orbital motion is adequately approximated by Newtonian Mechanics, historically, the apparent motions of the planets were described by European and Arabic philosophers using the idea of celestial spheres. This model posited the existence of perfect moving spheres or rings to which the stars and it assumed the heavens were fixed apart from the motion of the spheres, and was developed without any understanding of gravity. After the planets motions were accurately measured, theoretical mechanisms such as deferent. Originally geocentric it was modified by Copernicus to place the sun at the centre to help simplify the model, the model was further challenged during the 16th century, as comets were observed traversing the spheres. The basis for the understanding of orbits was first formulated by Johannes Kepler whose results are summarised in his three laws of planetary motion. Second, he found that the speed of each planet is not constant, as had previously been thought. Third, Kepler found a relationship between the orbital properties of all the planets orbiting the Sun. For the planets, the cubes of their distances from the Sun are proportional to the squares of their orbital periods. Jupiter and Venus, for example, are respectively about 5.2 and 0.723 AU distant from the Sun, their orbital periods respectively about 11.86 and 0.615 years. The proportionality is seen by the fact that the ratio for Jupiter,5. 23/11.862, is equal to that for Venus,0. 7233/0.6152. Idealised orbits meeting these rules are known as Kepler orbits, isaac Newton demonstrated that Keplers laws were derivable from his theory of gravitation and that, in general, the orbits of bodies subject to gravity were conic sections. Newton showed that, for a pair of bodies, the sizes are in inverse proportion to their masses. Where one body is more massive than the other, it is a convenient approximation to take the center of mass as coinciding with the center of the more massive body. Lagrange developed a new approach to Newtonian mechanics emphasizing energy more than force, in a dramatic vindication of classical mechanics, in 1846 le Verrier was able to predict the position of Neptune based on unexplained perturbations in the orbit of Uranus. This led astronomers to recognize that Newtonian mechanics did not provide the highest accuracy in understanding orbits, in relativity theory, orbits follow geodesic trajectories which are usually approximated very well by the Newtonian predictions but the differences are measurable. Essentially all the evidence that can distinguish between the theories agrees with relativity theory to within experimental measurement accuracy

6.
Sun
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The Sun is the star at the center of the Solar System. It is a perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99. 86% of the total mass of the Solar System. About three quarters of the Suns mass consists of hydrogen, the rest is mostly helium, with smaller quantities of heavier elements, including oxygen, carbon, neon. The Sun is a G-type main-sequence star based on its spectral class and it formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into a disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core and it is thought that almost all stars form by this process. The Sun is roughly middle-aged, it has not changed dramatically for more than four billion years and it is calculated that the Sun will become sufficiently large enough to engulf the current orbits of Mercury, Venus, and probably Earth. The enormous effect of the Sun on Earth has been recognized since prehistoric times, the synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today. The English proper name Sun developed from Old English sunne and may be related to south, all Germanic terms for the Sun stem from Proto-Germanic *sunnōn. The English weekday name Sunday stems from Old English and is ultimately a result of a Germanic interpretation of Latin dies solis, the Latin name for the Sun, Sol, is not common in general English language use, the adjectival form is the related word solar. The term sol is used by planetary astronomers to refer to the duration of a solar day on another planet. A mean Earth solar day is approximately 24 hours, whereas a mean Martian sol is 24 hours,39 minutes, and 35.244 seconds. From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, in the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton. The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna, in ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background, the symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions

7.
Planet
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The term planet is ancient, with ties to history, astrology, science, mythology, and religion. Several planets in the Solar System can be seen with the naked eye and these were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, in 2006, the International Astronomical Union officially adopted a resolution defining planets within the Solar System. This definition is controversial because it excludes many objects of mass based on where or what they orbit. The planets were thought by Ptolemy to orbit Earth in deferent, at about the same time, by careful analysis of pre-telescopic observation data collected by Tycho Brahe, Johannes Kepler found the planets orbits were not circular but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some shared such features as ice caps and seasons. Since the dawn of the Space Age, close observation by space probes has found that Earth and the planets share characteristics such as volcanism, hurricanes, tectonics. Planets are generally divided into two types, large low-density giant planets, and smaller rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System, in order of increasing distance from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four giant planets, Jupiter, Saturn, Uranus, and Neptune. Six of the planets are orbited by one or more natural satellites, several thousands of planets around other stars have been discovered in the Milky Way. e. in the habitable zone. On December 20,2011, the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets, Kepler-20e and Kepler-20f, orbiting a Sun-like star, Kepler-20. A2012 study, analyzing gravitational microlensing data, estimates an average of at least 1.6 bound planets for every star in the Milky Way, around one in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone. The idea of planets has evolved over its history, from the lights of antiquity to the earthly objects of the scientific age. The concept has expanded to include not only in the Solar System. The ambiguities inherent in defining planets have led to much scientific controversy, the five classical planets, being visible to the naked eye, have been known since ancient times and have had a significant impact on mythology, religious cosmology, and ancient astronomy. In ancient times, astronomers noted how certain lights moved across the sky, as opposed to the fixed stars, ancient Greeks called these lights πλάνητες ἀστέρες or simply πλανῆται, from which todays word planet was derived. In ancient Greece, China, Babylon, and indeed all pre-modern civilizations, it was almost universally believed that Earth was the center of the Universe and that all the planets circled Earth. The first civilization known to have a theory of the planets were the Babylonians

8.
Comet
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A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to evolve gasses, a process called outgassing. This produces an atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of collections of ice, dust. The coma may be up to 15 times the Earths diameter, if sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures, Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars, hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition, Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma and the tail, however, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System, the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. As of November 2014 there are 5,253 known comets, however, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System is estimated to be one trillion. Roughly one comet per year is visible to the eye, though many of those are faint. Particularly bright examples are called Great Comets, the word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a latinisation of the Greek κομήτης, Κομήτης was derived from κομᾶν, which was itself derived from κόμη and was used to mean the tail of a comet. The astronomical symbol for comets is ☄, consisting of a disc with three hairlike extensions. The solid, core structure of a comet is known as the nucleus, cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are described as dirty snowballs after Fred Whipples model

9.
International Astronomical Union
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The International Astronomical Union is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy. Among other activities, it acts as the recognized authority for assigning designations to celestial bodies. The IAU is a member of the International Council for Science and its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU maintains friendly relations with organizations that include amateur astronomers in their membership, the IAU has its head office on the second floor of the Institut dAstrophysique de Paris in the 14th arrondissement of Paris. The IAU is also responsible for the system of astronomical telegrams which are produced and distributed on its behalf by the Central Bureau for Astronomical Telegrams, the Minor Planet Center also operates under the IAU, and is a clearinghouse for all non-planetary or non-moon bodies in the Solar System. The Working Group for Meteor Shower Nomenclature and the Meteor Data Center coordinate the nomenclature of meteor showers, the IAU was founded on July 28,1919, at the Constitutive Assembly of the International Research Council held in Brussels, Belgium. The 7 initial member states were Belgium, Canada, France, Great Britain, Greece, Japan, the first executive committee consisted of Benjamin Baillaud, Alfred Fowler, and four vice presidents, William Campbell, Frank Dyson, Georges Lecointe, and Annibale Riccò. Thirty-two Commissions were appointed at the Brussels meeting and focused on topics ranging from relativity to minor planets, the reports of these 32 Commissions formed the main substance of the first General Assembly, which took place in Rome, Italy, May 2–10,1922. By the end of the first General Assembly, ten nations had joined the Union. Although the Union was officially formed eight months after the end of World War I, the first 50 years of the Unions history are well documented. Subsequent history is recorded in the form of reminiscences of past IAU Presidents, twelve of the fourteen past General Secretaries in the period 1964-2006 contributed their recollections of the Unions history in IAU Information Bulletin No.100. Six past IAU Presidents in the period 1976–2003 also contributed their recollections in IAU Information Bulletin No.104, the IAU includes a total of 12,664 individual members who are professional astronomers from 96 countries worldwide. 83% of all members are male, while 17% are female, among them the unions current president. Membership also includes 79 national members, professional astronomical communities representing their countrys affiliation with the IAU, the sovereign body of the IAU is its General Assembly, which comprises all members. The Assembly determines IAU policy, approves the Statutes and By-Laws of the Union, the right to vote on matters brought before the Assembly varies according to the type of business under discussion. On budget matters, votes are weighted according to the subscription levels of the national members. A second category vote requires a turnout of at least two-thirds of national members in order to be valid, an absolute majority is sufficient for approval in any vote, except for Statute revision which requires a two-thirds majority. An equality of votes is resolved by the vote of the President of the Union, since 1922, the IAU General Assembly meets every three years, with the exception of the period between 1938 and 1948, due to World War II

10.
IAU definition of planet
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A non-satellite body fulfilling only the first two of these criteria is classified as a dwarf planet. According to the IAU, planets and dwarf planets are two classes of objects. A non-satellite body fulfilling only the first criterion is termed a small Solar System body, an alternate proposal included dwarf planets as a subcategory of planets, but IAU members voted against this proposal. The definition was a one, and has drawn both support and criticism from different astronomers, but has remained in use. According to this definition, there are eight planets in the Solar System. The definition distinguishes planets from smaller bodies and is not useful outside the Solar System, extrasolar planets, or exoplanets, are covered separately under a complementary 2003 draft guideline for the definition of planets, which distinguishes them from dwarf stars, which are larger. Before the discoveries of the early 21st century, astronomers had no real need for a definition for planets. With the discovery of Pluto in 1930, astronomers considered the Solar System to have nine planets, along with thousands of bodies such as asteroids. Pluto was thought to be larger than Mercury, in 1978, the discovery of Plutos moon Charon radically changed this picture. By measuring Charons orbital period, astronomers could accurately calculate Plutos mass for the first time, in the 1990s, astronomers began finding other objects at least as far away as Pluto, now known as Kuiper Belt objects, or KBOs. Many of these some of Plutos key orbital characteristics and are now called plutinos. Pluto came to be seen as the largest member of a new class of objects, Plutos eccentric and inclined orbit, while very unusual for a planet in the Solar System, fits in well with the other KBOs. New York Citys newly renovated Hayden Planetarium did not include Pluto in its exhibit of the planets when it reopened as the Rose Center for Earth, astronomers also knew that more objects as large as Pluto would be discovered, and the number of planets would start growing quickly. They were also concerned about the classification of planets in other planetary systems, in 2006, the matter came to a head with the first measurement of the size of 2003 UB313. That measurement had showed Eris to appear to be larger than Pluto. The process of new discoveries spurring a contentious refinement of Plutos categorization echoed a debate in the 19th century that began with the discovery of Ceres on January 1,1801, astronomers immediately declared the tiny object to be the missing planet between Mars and Jupiter. Within four years, however, the discovery of two objects with comparable sizes and orbits had cast doubt on this new thinking. By 1851, the number of planets had grown to 23, astronomers began cataloguing them separately and began calling them asteroids instead of planets

11.
Small Solar System body
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A Small Solar System Body is an object in the Solar System that is neither a planet, nor a dwarf planet, nor a natural satellite. The term was first defined in 2006 by the International Astronomical Union, all other objects, except satellites, orbiting the Sun shall be referred to collectively as Small Solar System Bodies. These currently include most of the Solar System asteroids, most Trans-Neptunian Objects, comets and this encompasses all comets and all minor planets other than those that are dwarf planets. Except for the largest, which are in equilibrium, natural satellites differ from small Solar System bodies not in size. The orbits of satellites are not centered on the Sun, but around other Solar System objects such as planets, dwarf planets. Some of the larger small Solar System bodies may be reclassified in future as dwarf planets, the orbits of the vast majority of small Solar System bodies are located in two distinct areas, namely the asteroid belt and the Kuiper belt. These two belts possess some internal structure related to perturbations by the planets, and have fairly loosely defined boundaries. Other areas of the Solar System also encompass small bodies in smaller concentrations and these include the near-Earth asteroids, centaurs, comets, and scattered disc objects

12.
Asteroid
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Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids and these terms have historically been applied to any astronomical object orbiting the Sun that did not show the disc of a planet and was not observed to have the characteristics of an active comet. As minor planets in the outer Solar System were discovered and found to have volatile-based surfaces that resemble those of comets, in this article, the term asteroid refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There are millions of asteroids, many thought to be the remnants of planetesimals. The large majority of known asteroids orbit in the belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects, individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups, C-type, M-type, and S-type. These were named after and are identified with carbon-rich, metallic. The size of asteroids varies greatly, some reaching as much as 1000 km across, asteroids are differentiated from comets and meteoroids. In the case of comets, the difference is one of composition, while asteroids are composed of mineral and rock, comets are composed of dust. In addition, asteroids formed closer to the sun, preventing the development of the aforementioned cometary ice, the difference between asteroids and meteoroids is mainly one of size, meteoroids have a diameter of less than one meter, whereas asteroids have a diameter of greater than one meter. Finally, meteoroids can be composed of either cometary or asteroidal materials, only one asteroid,4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be visible to the eye for a short time. As of March 2016, the Minor Planet Center had data on more than 1.3 million objects in the inner and outer Solar System, the United Nations declared June 30 as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, the first asteroid to be discovered, Ceres, was found in 1801 by Giuseppe Piazzi, and was originally considered to be a new planet. In the early half of the nineteenth century, the terms asteroid. Asteroid discovery methods have improved over the past two centuries. This task required that hand-drawn sky charts be prepared for all stars in the band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, the expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers

13.
Trojan (astronomy)
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In astronomy, a trojan is a minor planet or moon that shares the orbit of a planet or larger moon, wherein the trojan remains in the same, stable position relative to the larger object. In particular, a trojan remains near one of the two points of stability – designated L4 and L5 – which lie approximately 60° ahead of and behind the larger body. Trojan points make up two of five types of Lagrangian points, and a trojan is a type of Lagrangian object and they are one type of co-orbital object. In this arrangement, the star and the smaller planet orbit about their common barycenter. A much smaller mass located at one of the Lagrangian points is subject to a gravitational force that acts through this barycenter. Hence the object can orbit around the barycenter with the orbital period as the planet. The Jupiter trojans account for most known trojans in the Solar System and they are divided into the Greek camp in front of and the Trojan camp trailing behind Jupiter in their orbit. Numerical calculations of the dynamics involved indicate that Saturn and Uranus probably do not have any primordial trojans. The discovery of the first Earth trojan,2010 TK7, was announced by NASA in 2011, unlike trojan minor planets that share the orbit with a planet, a trojan moon is a moon orbiting near the trojan point of another, larger moon. All known trojan moons are part of the Saturn system, telesto and Calypso are trojans of Tethys, and Helene and Polydeuces of Dione. There is also a concept of a trojan planet, a planet that orbits at the trojan point of another, larger planet. Such a pair of co-orbital exoplanets was already thought to exist in another star system, in 1772, the Italian–French mathematician and astronomer Joseph-Louis Lagrange obtained two constant-pattern solutions of the general three-body problem. In the restricted problem, with one mass negligible, the five possible positions of that mass are now termed Lagrangian points. The term trojan originally referred to the asteroids that orbit close to the Lagrangian points of Jupiter. These have long been named after characters from the Trojan War of Greek mythology, there are two exceptions, which were named before the convention was put in place, the Greek-themed 617 Patroclus and the Trojan-themed 624 Hektor, which were assigned to the wrong sides. Astronomers estimate that the Jupiter trojans are about as numerous as the asteroids of the asteroid belt, later on, objects were found orbiting near the Lagrangian points of Neptune, Mars, Earth, Uranus, and Venus. Minor planets at the Lagrangian points of other than Jupiter may be called Lagrangian minor planets. 17 Neptune trojans are known, but large Neptune trojans are expected to outnumber the large Jupiter trojans by an order of magnitude,2010 TK7 was confirmed to be the first known Earth trojan in 2011

14.
Centaur (minor planet)
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Centaurs are minor planets with a semi-major axis between those of the outer planets. They have unstable orbits that cross or have crossed the orbits of one or more of the giant planets, Centaurs typically behave with characteristics of both asteroids and comets. They are named after the centaurs that were a mixture of horse. It has been estimated there are around 44,000 centaurs in the Solar System with diameters larger than 1 km. The first centaur to be discovered, under the definition of the Jet Propulsion Laboratory, however, they were not recognized as a distinct population until the discovery of 2060 Chiron in 1977. The largest confirmed centaur is 10199 Chariklo, which at 260 km in diameter is as big as a mid-sized main-belt asteroid, however, the lost centaur 1995 SN55 may be somewhat larger. No centaur has been photographed up close, although there is evidence that Saturns moon Phoebe, imaged by the Cassini probe in 2004, in addition, the Hubble Space Telescope has gleaned some information about the surface features of 8405 Asbolus. As of 2008, three centaurs have been found to display comet-like comas, Chiron,60558 Echeclus, and 166P/NEAT, Chiron and Echeclus are therefore classified as both asteroids and comets. Other centaurs, such as 52872 Okyrhoe and 2012 CG, are suspected of having shown comas, any centaur that is perturbed close enough to the Sun is expected to become a comet. The generic definition of a centaur is a body that orbits the Sun between Jupiter and Neptune and crosses the orbits of one or more of the giant planets. Though nowadays the MPC often lists centaurs and scattered disc objects together as a single group, the Jet Propulsion Laboratory similarly defines centaurs as having a semi-major axis, a, between those of Jupiter and Neptune. In contrast, the Deep Ecliptic Survey defines centaurs using a classification scheme. These classifications are based on the change in behavior of the present orbit when extended over 10 million years. The DES defines centaurs as non-resonant objects whose instantaneous perihelia are less than the osculating semi-major axis of Neptune at any time during the simulation and this definition is intended to be synonymous with planet-crossing orbits and to suggest comparatively short lifetimes in the current orbit. The collection The Solar System Beyond Neptune defines objects with an axis between those of Jupiter and Neptune and a Jupiter – Tisserands parameter above 3. The JPL Small-Body Database lists 324 centaurs, there are an additional 65 trans-Neptunian objects with a perihelion closer than the orbit of Uranus. The Committee on Small Body Nomenclature of the International Astronomical Union has not formally weighed in on either side of the debate, thus far, only the binary objects Ceto and Phorcys and Typhon and Echidna have been named according to the new policy. Other objects caught between these differences in classification methods include 944 Hidalgo which was discovered in 1920 and is listed as a centaur in the JPL Small-Body Database

15.
Kuiper belt
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It is similar to the asteroid belt, but it is far larger—20 times as wide and 20 to 200 times as massive. Like the asteroid belt, it consists mainly of small bodies, although many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles, such as methane, ammonia and water. The Kuiper belt is home to three officially recognized dwarf planets, Pluto, Haumea, and Makemake, some of the Solar Systems moons, such as Neptunes Triton and Saturns Phoebe, are also thought to have originated in the region. The Kuiper belt was named after Dutch-American astronomer Gerard Kuiper, though he did not actually predict its existence, in 1992,1992 QB1 was discovered, the first Kuiper belt object since Pluto. Since its discovery, the number of known KBOs has increased to over a thousand, the Kuiper belt should not be confused with the theorized Oort cloud, which is a thousand times more distant and is mostly spherical. The objects within the Kuiper belt, together with the members of the scattered disc, Pluto is the largest and most-massive member of the Kuiper belt and the largest and the second-most-massive known TNO, surpassed only by Eris in the scattered disc. Originally considered a planet, Plutos status as part of the Kuiper belt caused it to be reclassified as a planet in 2006. It is compositionally similar to other objects of the Kuiper belt, and its orbital period is characteristic of a class of KBOs, known as plutinos. After the discovery of Pluto in 1930, many speculated that it not be alone. The region now called the Kuiper belt was hypothesized in various forms for decades and it was only in 1992 that the first direct evidence for its existence was found. The number and variety of speculations on the nature of the Kuiper belt have led to continued uncertainty as to who deserves credit for first proposing it. The first astronomer to suggest the existence of a population was Frederick C. That same year, astronomer Armin O. Leuschner suggested that Pluto may be one of many long-period planetary objects yet to be discovered. Kuiper was operating on the common in his time that Pluto was the size of Earth and had therefore scattered these bodies out toward the Oort cloud or out of the Solar System. Were Kuipers hypothesis correct, there would not be a Kuiper belt today, the hypothesis took many other forms in the following decades. Cameron postulated the existence of a mass of small material on the outskirts of the solar system. Observation, however, ruled out this hypothesis, in 1977, Charles Kowal discovered 2060 Chiron, an icy planetoid with an orbit between Saturn and Uranus. He used a blink comparator, the device that had allowed Clyde Tombaugh to discover Pluto nearly 50 years before

16.
Trans-Neptunian object
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A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune,30 astronomical units. Twelve minor planets with a semi-major axis greater than 150 AU and perihelion greater than 30 AU are known, the first trans-Neptunian object to be discovered was Pluto in 1930. It took until 1992 to discover a second trans-Neptunian object orbiting the Sun directly,1992 QB1, as of February 2017 over 2,300 trans-Neptunian objects appear on the Minor Planet Centers List of Transneptunian Objects. Of these TNOs,2,000 have a perihelion farther out than Neptune, as of November 2016,242 of these have their orbits well-enough determined that they have been given a permanent minor planet designation. The largest known object is Pluto, followed by Eris,2007 OR10, Makemake. The Kuiper belt, scattered disk, and Oort cloud are three divisions of this volume of space, though treatments vary and a few objects such as Sedna do not fit easily into any division. The orbit of each of the planets is slightly affected by the influences of the other planets. Discrepancies in the early 1900s between the observed and expected orbits of Uranus and Neptune suggested that there were one or more additional planets beyond Neptune, the search for these led to the discovery of Pluto in February 1930, which was too small to explain the discrepancies. Revised estimates of Neptunes mass from the Voyager 2 flyby in 1989 showed that the problem was spurious, Pluto was easiest to find because it has the highest apparent magnitude of all known trans-Neptunian objects. It also has an inclination to the ecliptic than most other large TNOs. After Plutos discovery, American astronomer Clyde Tombaugh continued searching for years for similar objects. For a long time, no one searched for other TNOs as it was believed that Pluto. Only after the 1992 discovery of a second TNO,1992 QB1, a broad strip of the sky around the ecliptic was photographed and digitally evaluated for slowly moving objects. Hundreds of TNOs were found, with diameters in the range of 50 to 2,500 kilometers, Pluto and Eris were eventually classified as dwarf planets by the International Astronomical Union. Kuiper belt objects are classified into the following two groups, Resonant objects are locked in an orbital resonance with Neptune. Objects with a 1,2 resonance are called twotinos, and objects with a 2,3 resonance are called plutinos, after their most prominent member, classical Kuiper belt objects have no such resonance, moving on almost circular orbits, unperturbed by Neptune. Examples are 1992 QB1,50000 Quaoar and Makemake, the scattered disc contains objects farther from the Sun, usually with very irregular orbits. A typical example is the most massive known TNO, Eris, scattered-extended —Scattered-extended objects have a Tisserand parameter greater than 3 and have a time-averaged eccentricity greater than 0

17.
Ceres (dwarf planet)
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Ceres is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter. Its diameter is approximately 945 kilometers, making it the largest of the planets within the orbit of Neptune. The 33rd-largest known body in the Solar System, it is the dwarf planet within the orbit of Neptune. Composed of rock and ice, Ceres is estimated to approximately one third of the mass of the entire asteroid belt. Ceres is the object in the asteroid belt known to be rounded by its own gravity. From Earth, the apparent magnitude of Ceres ranges from 6.7 to 9.3, Ceres was the first asteroid discovered, by Giuseppe Piazzi at Palermo on 1 January 1801. It was originally considered a planet, but was reclassified as an asteroid in the 1850s after many other objects in similar orbits were discovered. Ceres appears to be differentiated into a core and icy mantle. The surface is probably a mixture of ice and various hydrated minerals such as carbonates. In January 2014, emissions of water vapor were detected from several regions of Ceres and this was unexpected, because large bodies in the asteroid belt typically do not emit vapor, a hallmark of comets. The robotic NASA spacecraft Dawn entered orbit around Ceres on 6 March 2015, pictures with a resolution previously unattained were taken during imaging sessions starting in January 2015 as Dawn approached Ceres, showing a cratered surface. Two distinct bright spots inside a crater were seen in a 19 February 2015 image, on 11 May 2015, NASA released a higher-resolution image showing that, instead of one or two spots, there are actually several. In October 2015, NASA released a true portrait of Ceres made by Dawn. In February 2017, organics were reported to have been detected on Ceres in Ernutet crater, Johann Elert Bode, in 1772, first suggested that an undiscovered planet could exist between the orbits of Mars and Jupiter. Kepler had already noticed the gap between Mars and Jupiter in 1596, the pattern predicted that the missing planet ought to have an orbit with a semi-major axis near 2.8 astronomical units. Although they did not discover Ceres, they found several large asteroids. One of the selected for the search was Giuseppe Piazzi. Before receiving his invitation to join the group, Piazzi discovered Ceres on 1 January 1801 and he was searching for the 87th of the Catalogue of the Zodiacal stars of Mr la Caille, but found that it was preceded by another

18.
Jupiter
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Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass one-thousandth that of the Sun, Jupiter and Saturn are gas giants, the other two giant planets, Uranus and Neptune are ice giants. Jupiter has been known to astronomers since antiquity, the Romans named it after their god Jupiter. Jupiter is primarily composed of hydrogen with a quarter of its mass being helium and it may also have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid surface. Because of its rotation, the planets shape is that of an oblate spheroid. The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence, a prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding Jupiter is a faint planetary ring system and a powerful magnetosphere, Jupiter has at least 67 moons, including the four large Galilean moons discovered by Galileo Galilei in 1610. Ganymede, the largest of these, has a greater than that of the planet Mercury. Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter. In late February 2007, Jupiter was visited by the New Horizons probe, the latest probe to visit the planet is Juno, which entered into orbit around Jupiter on July 4,2016. Future targets for exploration in the Jupiter system include the probable ice-covered liquid ocean of its moon Europa, Earth and its neighbor planets may have formed from fragments of planets after collisions with Jupiter destroyed those super-Earths near the Sun. Astronomers have discovered nearly 500 planetary systems with multiple planets, Jupiter moving out of the inner Solar System would have allowed the formation of inner planets, including Earth. Jupiter is composed primarily of gaseous and liquid matter and it is the largest of the four giant planets in the Solar System and hence its largest planet. It has a diameter of 142,984 km at its equator, the average density of Jupiter,1.326 g/cm3, is the second highest of the giant planets, but lower than those of the four terrestrial planets. Jupiters upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules, a helium atom has about four times as much mass as a hydrogen atom, so the composition changes when described as the proportion of mass contributed by different atoms. Thus, Jupiters atmosphere is approximately 75% hydrogen and 24% helium by mass, the atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds. There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, the outermost layer of the atmosphere contains crystals of frozen ammonia. The interior contains denser materials - by mass it is roughly 71% hydrogen, 24% helium, through infrared and ultraviolet measurements, trace amounts of benzene and other hydrocarbons have also been found

19.
Hydrostatic equilibrium
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In fluid mechanics, a fluid is said to be in hydrostatic equilibrium or hydrostatic balance when it is at rest, or when the flow velocity at each point is constant over time. This occurs when external forces such as gravity are balanced by a pressure gradient force, hydrostatic equilibrium is the current distinguishing criterion between dwarf planets and small Solar System bodies, and has other roles in astrophysics and planetary geology. This qualification typically means that the object is symmetrically rounded into a spheroid or ellipsoid shape, there are 31 observationally confirmed such objects, sometimes called planemos, in the Solar System, seven more that are virtually certain, and a hundred or so more that are likely. Newtons laws of state that a volume of a fluid that is not in motion or that is in a state of constant velocity must have zero net force on it. This means the sum of the forces in a given direction must be opposed by a sum of forces in the opposite direction. This force balance is called a hydrostatic equilibrium, the fluid can be split into a large number of cuboid volume elements, by considering a single element, the action of the fluid can be derived. If the density is ρ, the volume is V and g the standard gravity, then, the volume of this cuboid is equal to the area of the top or bottom, times the height — the formula for finding the volume of a cube. This sum equals zero if the velocity is constant. Dividing by A,0 = P b o t t o m − P t o p − ρ ⋅ g ⋅ h, or, P t o p − P b o t t o m = − ρ ⋅ g ⋅ h. Ptop − Pbottom is a change in pressure, and h is the height of the volume change in the distance above the ground. By saying these changes are small, the equation can be written in differential form. Density changes with pressure, and gravity changes with height, so the equation would be, d P = − ρ ⋅ g ⋅ d h. Note finally that this last equation can be derived by solving the three-dimensional Navier–Stokes equations for the situation where u = v = ∂ p ∂ x = ∂ p ∂ y =0. Then the only equation is the z -equation, which now reads ∂ p ∂ z + ρ g =0. Thus, hydrostatic balance can be regarded as a simple equilibrium solution of the Navier–Stokes equations. M is a foliation of spheres weighted by the mass density ρ, the hydrostatic equilibrium pertains to hydrostatics and the principles of equilibrium of fluids. A hydrostatic balance is a balance for weighing substances in water. Hydrostatic balance allows the discovery of their specific gravities, in any given layer of a star, there is a hydrostatic equilibrium between the outward thermal pressure from below and the weight of the material above pressing inward

20.
Ellipsoid
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An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a surface, that is a surface that may be defined as the zero set of a polynomial of degree two in three variables. Among quadric surfaces, an ellipsoid is characterized by any of the two following properties, every planar cross section is either an ellipse, or is empty, or is reduced to a single point. It is bounded, which means that it may be enclosed in a large sphere. An ellipsoid has three perpendicular axes of symmetry which intersect at a center of symmetry, called the center of the ellipsoid. The line segments that are delimited on the axes of symmetry by the ellipsoid are called the principal axes, if the three axes have different lengths, the ellipsoid is said to be tri-axial or scalene, and the axes are uniquely defined. If two of the axes have the length, then the ellipsoid is an ellipsoid of revolution. In this case, the ellipsoid is invariant under a rotation around the third axis, if the third axis is shorter, the ellipsoid is an oblate spheroid, if it is longer, it is prolate spheroid. If the three axes have the length, the ellipsoid is a sphere. The points, and lie on the surface, the line segments from the origin to these points are called the semi-principal axes of the ellipsoid, because a, b, c are half the length of the principal axes. They correspond to the axis and semi-minor axis of an ellipse. If a = b > c, one has an oblate spheroid, if a = b < c, one has a prolate spheroid, if a = b = c, one has a sphere. It is easy to check, The intersection of a plane, remark, The contour of an ellipsoid, seen from a point outside the ellipsoid or from infinity, is in any case a plane section, hence an ellipse. The ellipsoid may be parameterized in several ways, which are simpler to express when the ellipsoid axes coincide with coordinate axes. A common choice is x = a cos ⁡ cos ⁡, y = b cos ⁡ sin ⁡, z = c sin ⁡ and these parameters may be interpreted as spherical coordinates. More precisely, π /2 − θ is the polar angle, and φ is the azimuth angle of the point of the ellipsoid. More generally, an arbitrarily oriented ellipsoid, centered at v, is defined by the x to the equation T A =1. The eigenvectors of A define the axes of the ellipsoid and the eigenvalues of A are the reciprocals of the squares of the semi-axes

21.
Near-Earth object
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A near-Earth object is any small Solar System body whose orbit brings it into proximity with Earth. By definition, a solar system body is a NEO if its closest approach to the Sun is less than 1.3 astronomical unit and it is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the Earth. NEOs have become of increased interest since the 1980s because of increased awareness of the potential danger some of the asteroids or comets pose, and mitigations are being researched. In January 2016, NASA announced the Planetary Defense Coordination Office to track NEOs larger than 30 to 50 meters in diameter and coordinate an effective threat response, NEAs have orbits that lie partly between 0.983 and 1.3 AU away from the Sun. When a NEA is detected it is submitted to the IAUs Minor Planet Center for cataloging, some NEAs orbits intersect that of Earths so they pose a collision danger. The United States, European Union, and other nations are currently scanning for NEOs in an effort called Spaceguard. In the United States and since 1998, NASA has a mandate to catalogue all NEOs that are at least 1 kilometer wide. In 2006, it was estimated that 20% of the objects had not yet been found. In 2011, largely as a result of NEOWISE, it was estimated that 93% of the NEAs larger than 1 km had been found, as of 5 February 2017, there have been 875 NEAs larger than 1 km discovered, of which 157 are potentially hazardous. The inventory is much less complete for smaller objects, which still have potential for scale, though not global. Potentially hazardous objects are defined based on parameters that measure the objects potential to make threatening close approaches to the Earth. Mostly objects with an Earth minimum orbit intersection distance of 0.05 AU or less, objects that cannot approach closer to the Earth than 0.05 AU, or are smaller than about 150 m in diameter, are not considered PHOs. This makes them a target for exploration. As of 2016, three near-Earth objects have been visited by spacecraft, more recently, a typical frame of reference for looking at NEOs has been through the scientific concept of risk. In this frame, the risk that any near-Earth object poses is typically seen through a lens that is a function of both the culture and the technology of human society, NEOs have been understood differently throughout history. Each time an NEO is observed, a different risk was posed and it is not just a matter of scientific knowledge. Such perception of risk is thus a product of religious belief, philosophic principles, scientific understanding, technological capabilities, and even economical resourcefulness.03 E −0.4 megatonnes. For instance, it gives the rate for bolides of 10 megatonnes or more as 1 per thousand years, however, the authors give a rather large uncertainty, due in part to uncertainties in determining the energies of the atmospheric impacts that they used in their determination

22.
Aten asteroid
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The Aten asteroids are a group of asteroids, whose orbit brings them into proximity with Earth. The group is named after 2062 Aten, the first of its kind, since then, more than 1,000 Atens have been discovered, of which many are classified as potentially hazardous asteroids. For a list of existing articles, see Aten asteroids and List of Aten asteroids, Aten asteroids are defined by having a semi-major axis of less than one astronomical unit, the average distance from the Earth to the Sun. They also have a greater than 0.983 AU. Asteroids orbits can be highly eccentric, an Aten orbit need not be entirely contained within Earths orbit, as nearly all known Aten asteroids have their aphelion greater than 1 AU although their semi-major axis is less than 1 AU. Observation of objects inferior to the Earths orbit is difficult and this difficulty may be the cause of some sampling bias in the apparent preponderance of eccentric Atens, Aten asteroids account for only about 6% of the known near-Earth asteroid population. Many more Apollo-class asteroids are known than Aten-class asteroids, possibly because of the sampling bias, the shortest semi-major axis for any known Aten asteroid is 2008 EY5 at 0.626 AU. A very small possibility of impact remained for 2036, but this was also eliminated, there are also sixteen known Apohele asteroids, traditionally listed as a subclass of Atens, but generally regarded a separate class of their own. Unlike Atens, Apoheles permanently stay within Earths orbit and do not cross it

23.
Apollo asteroid
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The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth crossing asteroids that have an orbital semi-major axis greater than that of the Earth, as of November 2016, the steadily growing number of known Apollo asteroids has reached a total of 8,180 members. It is by far the largest group of objects, compared to the Aten, Amor. Currently, there are 1,133 numbered Apollos, asteroids are not numbered until they have been observed at two or more oppositions. There are also 1,472 Apollo asteroids that are enough. The closer their semi-major axis is to Earths, the eccentricity is needed for the orbits to cross. The largest known Apollo asteroid is 1866 Sisyphus, with a diameter of about 8.5 km, examples of known Apollo asteroids include, Apollo asteroids Apollo asteroid records List of Apollo minor planets

24.
Earth-crosser asteroid
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An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earths orbit. The known numbered Earth-crossers are listed here and those Earth-crossers whose semi-major axes are smaller than Earths are Aten asteroids, the remaining ones are Apollo asteroids. An asteroid with an Earth-crossing orbit is not necessarily in danger of colliding with Earth, the orbit of an Earth-crossing asteroid may not even intersect with that of Earth. This apparent contradiction arises because many asteroids have highly inclined orbits, so although they may have a less than that of Earth. An asteroid for which there is possibility of a collision with Earth at a future date. Specifically, an asteroid is a PHA if its Earth minimum orbital intersection distance is <0.05 AU, the concept of PHA is intended to replace the now abandoned strict definition of ECA which existed for a few years. Having a small MOID is not a guarantee of a collision, on the other hand, small gravitational perturbations of the asteroid around its orbit from planets that it passes can significantly alter its path. For instance,99942 Apophis will approach Earth so closely in 2029 that it will get under the orbit of the Earths geostationary satellites, the Earth will change the trajectory of Apophis and the result may be an even closer approach in the future, possibly 2036. Of the Earth-crossing asteroids,3753 Cruithne is notable for having an orbit that has the period as Earths.2 AU

25.
Amor asteroid
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The Amor asteroids are a group of near-Earth asteroids named after the asteroid 1221 Amor. They approach the orbit of Earth from beyond, but do not cross it, most Amors cross the orbit of Mars. The two moons of Mars, Deimos and Phobos, may be Amor asteroids that were captured by Marss gravity, the most famous member of this group is 433 Eros, which was the first asteroid to be orbited and then landed upon by a human probe. There are three general criteria which an asteroid must meet to be considered a member of the Amor asteroid class, to be considered near, the asteroid must come closer to Earth than to any other major planet. The closest planet to Earth is Venus, which can come as close as 0.27 AU, therefore, an Amor asteroid must come within 0.30 AU of Earths orbit. The asteroids orbit must be outside the orbit of Earth, asteroids that come close to Earth whose orbits are inside Earths orbit are considered Apohele asteroids. The asteroids orbit must not cross Earths orbit, the most commonly used definition of this is that it never orbits closer to the Sun than Earths average distance from the Sun. A more strict definition is that at any point along the asteroids orbit and this takes into consideration the fact that Earths orbit ranges between 0.983 and 1.016 AU from the Sun. It is more difficult to sort out the Amor asteroids from the non-Amor asteroids using this definition, however. These three criteria boil down to a single test for membership, If an asteroid has a perihelion between 1.000 AU and 1.300 AU, it is an Amor asteroid. Any asteroid with this trait is considered an Amor-class asteroid, regardless of its axis, eccentricity, aphelion, inclination, physical properties, orbital stability. An asteroid belongs to the Amor group if, Its orbital period is greater than one year and this is equivalent to saying that its semi-major axis is greater than 1.0 AU. Its orbit does not cross Earths orbit and that is, its lowest point is higher than Earths highest point. It is an object, that is, its perihelion distance q <1.3 AU. In summary, a >1.0 AU and 1.017 AU < q <1.3 AU, there are 6051 Amor asteroids currently known. 960 of them are numbered, and 73 of them are named, Amor asteroids can be partitioned into four subgroups, depending on their average distance from the Sun. The Amor I subgroup consists of Amor asteroids whose semi-major axes are in between Earth and Mars and that is, they have a semi-major axis between 1.000 and 1.523 AU. Less than one fifth of Amor asteroids belong to this subgroup, Amor I asteroids have lower eccentricities than the other subgroups of Amors

26.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun

27.
Earth trojan
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An Earth trojan is an asteroid that orbits the Sun in the vicinity of the Earth–Sun Lagrangian points L4 and L5, thus having an orbit similar to Earths. Only one Earth trojan has so far been discovered, the name trojan was first used in 1906 for the Jupiter trojans, the asteroids that were observed near the Lagrangian points of Jupiters orbit. Current L42010 TK7, A 300-meter-diameter asteroid, discovered using the Wide-field Infrared Survey Explorer satellite and it is the only confirmed Earth trojan as of 2011–2012. L5 No known objects are thought to be L5 trojans of Earth. 2010 TK7 was discovered using the Wide-field Infrared Survey Explorer satellite, in February 2017, the OSIRIS-REx spacecraft performed a search from within the L4 region on its way to asteroid Bennu. The orbits of any Earth trojans could make them less costly to reach than the Moon. Such asteroids could one day be useful as sources of elements that are rare near Earths surface, on Earth, siderophiles such as iridium are difficult to find, having largely sunk to the core of the planet shortly after its formation. A hypothetical planet-sized Earth trojan the size of Mars, given the name Theia, is thought by proponents of the hypothesis to be the origin of the Moon. The hypothesis states that the Moon formed after Earth and Theia collided head-on and this material eventually accreted around Earth and into a single orbiting body, the Moon. At the same time, material from Theia mixed and combined with Earths mantle, supporters of the giant-impact hypothesis theorise that Earths large core in relation to its overall volume is as a result of this combination. Several other small objects have found on an orbital path associated with Earth. Although these objects are in 1,1 orbital resonance, they are not Earth trojans because they do not librate around a definite Sun–Earth Lagrangian point, Earth has another noted companion, asteroid 3753 Cruithne. About 5 km across, it has a type of orbital resonance called an overlapping horseshoe. 2016 HO3, an asteroid discovered on 27 April 2016, is possibly the most stable quasi-satellite of Earth

28.
2010 TK7
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2010 TK7 is a near-Earth asteroid and the first Earth trojan discovered, it precedes Earth in its orbit around the Sun. Trojan objects are most easily conceived as orbiting at a Lagrangian point, in reality, they oscillate around such a point. Such objects had previously observed in the orbits of Mars, Jupiter, Neptune. 2010 TK7 has a diameter of about 300 meters and its path oscillates about the Sun–Earth L4 Lagrangian point, shuttling between its closest approach to Earth and its closest approach to the L3 point about every 400 years. The asteroid was discovered in October 2010 by the NEOWISE team of astronomers using NASAs Wide-field Infrared Survey Explorer. WISE, a space telescope launched into Earth orbit in December 2009, spotting an asteroid sharing Earths orbit is normally difficult from the ground, because their potential locations are generally in the daytime sky. After follow-up work at the University of Hawaii and the Canada–France–Hawaii Telescope, its orbit was evaluated on 21 May 2011,2010 TK7 has an absolute magnitude of luminosity of about 20.8. Based on an assumed albedo of 0.1, its diameter is about 300 meters. No spectral data are yet available to shed light on its composition,2010 TK7 would exert a surface gravitational force of less than 1/20,000 times that of Earth. At the time of discovery, the asteroid orbited the Sun with a period of 365.389 days, as long as it remains in 1,1 resonance with Earth, its average period over long time intervals will exactly equal that of Earth. On its eccentric orbit,2010 TK7s distance from the Sun varies annually from 0.81 AU to 1.19 AU and it orbits in a plane inclined about 21 degrees to the plane of the ecliptic. Trojans do not orbit right at Lagrangian points but oscillate in tadpole-shaped loops around them,2010 TK7 traverses its loop over a period of 395 years,2010 TK7s loop is so elongated that it sometimes travels nearly to the opposite side of the Sun with respect to Earth. Its movements do not bring it any closer to Earth than 20 million kilometers, in 2010/2011,2010 TK7 was at the near-Earth end of its tadpole, which facilitated its discovery. 2010 TK7s orbit has a character, making long-range predictions difficult. Prior to 500 AD, it may have been oscillating about the L5 Lagrangian point, short-term unstable libration about L3, and transitions to horseshoe orbits are also possible.4 km/s, whereas some other near-Earth asteroids require less than 4 km/s. During the 5 December 2012 Earth close approach of 0.197 AU, claimed moons of Earth Provisional designation in astronomy, the naming convention used for astronomical objects immediately following their discovery Amos, Jonathan. Trojan asteroid seen in Earths orbit by Wise telescope

29.
Mars trojan
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The Mars trojans are a group of objects that share the orbit of the planet Mars around the Sun. They can be found around the two Lagrangian points 60° ahead of and behind Mars, the origin of the Mars trojans is not well understood. One theory suggests that they were captured in its Lagrangian points as the Solar System was forming, however, spectral studies of the Mars trojans indicate this may not be the case. One explanation for this involves asteroids wandering into the Mars Lagrangian points later in the Solar Systems formation and this is also questionable considering the very low mass of Mars

30.
Asteroid belt
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The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets, the asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, the total mass of the asteroid belt is approximately 4% that of the Moon, or 22% that of Pluto, and roughly twice that of Plutos moon Charon. Ceres, the belts only dwarf planet, is about 950 km in diameter, whereas Vesta, Pallas. The remaining bodies range down to the size of a dust particle, the asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, and these can form a family whose members have similar orbital characteristics. Individual asteroids within the belt are categorized by their spectra. The asteroid belt formed from the solar nebula as a group of planetesimals. Planetesimals are the precursors of the protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals, as a result,99. 9% of the asteroid belts original mass was lost in the first 100 million years of the Solar Systems history. Some fragments eventually found their way into the inner Solar System, Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits. Classes of small Solar System bodies in other regions are the objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids. On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on Ceres, the detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding was unexpected because comets, not asteroids, are considered to sprout jets. According to one of the scientists, The lines are becoming more and more blurred between comets and asteroids. This pattern, now known as the Titius–Bode law, predicted the semi-major axes of the six planets of the provided one allowed for a gap between the orbits of Mars and Jupiter

31.
Jupiter trojan
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The Jupiter trojans, commonly called Trojan asteroids or just Trojans, are a large group of asteroids that share the orbit of the planet Jupiter around the Sun. Relative to Jupiter, each Trojan librates around one of Jupiters two stable Lagrangian points, L4, lying 60° ahead of the planet in its orbit, and L5, 60° behind. Jupiter trojans are distributed in two elongated, curved regions around these Lagrangian points with an average axis of about 5.2 AU. The first Jupiter trojan discovered,588 Achilles, was spotted in 1906 by German astronomer Max Wolf, a total of 6,178 Jupiter trojans have been found as of January 2015. By convention they are named after a mythological figure from the Trojan War. The total number of Jupiter trojans larger than 1 km in diameter is believed to be about 1 million, like main-belt asteroids, Jupiter trojans form families. Jupiter trojans are bodies with reddish, featureless spectra. The Jupiter trojans densities vary from 0.8 to 2.5 g·cm−3, Jupiter trojans are thought to have been captured into their orbits during the early stages of the Solar Systems formation or slightly later, during the migration of giant planets. NASA has announced the discovery of an Earth trojan, the trapped body will librate slowly around the point of equilibrium in a tadpole or horseshoe orbit. These leading and trailing points are called the L4 and L5 Lagrange points, however, no asteroids trapped in Lagrange points were observed until more than a century after Lagranges hypothesis. Those associated with Jupiter were the first to be discovered, E. E. Barnard made the first recorded observation of a Trojan,1999 RM11, in 1904, but neither he nor others appreciated its significance at the time. Barnard believed he saw the recently discovered Saturnian satellite Phoebe, which was only two away in the sky at the time, or possibly an asteroid. The objects identity was not realized until its orbit was calculated in 1999, in 1906–1907 two more Jupiter trojans were found by fellow German astronomer August Kopff. Hektor, like Achilles, belonged to the L4 swarm, whereas Patroclus was the first asteroid known to reside at the L5 Lagrangian point, by 1938,11 Jupiter trojans had been detected. This number increased to 14 only in 1961, as instruments improved, the rate of discovery grew rapidly, by January 2000, a total of 257 had been discovered, by May 2003, the number had grown to 1,600. Asteroids in the L4 group are named after Greek heroes, confusingly,617 Patroclus was named before the Greece/Troy rule was devised, and a Greek name thus appears in the Trojan node. The Greek node also has one misplaced asteroid,624 Hektor, estimates of the total number of Jupiter trojans are based on deep surveys of limited areas of the sky. The L4 swarm is believed to hold between 160–240,000 asteroids with diameters larger than 2 km and about 600,000 with diameters larger than 1 km

32.
Neptune trojan
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Neptune trojans are bodies in orbit around the Sun that orbit near one of the stable Lagrangian points of Neptune. They therefore have approximately the same period as Neptune and follow roughly the same orbital path. Seventeen Neptune trojans are known, of which thirteen orbit near the Sun–Neptune L4 Lagrangian point 60° ahead of Neptune. The Neptune trojans are termed trojans by analogy with the Jupiter trojans and it is suspected that large Neptune trojans could outnumber Jupiter trojans by an order of magnitude. In 2010, the discovery of the first known L5 Neptune trojan,2008 LC18, was announced, Neptunes trailing L5 region is currently very difficult to observe because it is along the line-of-sight to the center of the Milky Way, an area of the sky crowded with stars. However, New Horizons may not have had sufficient downlink bandwidth, in 2001, the first Neptune trojan was discovered,2001 QR322, near Neptunes L4 region, and with it the fifth known populated stable reservoir of small bodies in the Solar System. In 2005, the discovery of the high-inclination trojan 2005 TN53 has indicated that the Neptune trojans populate thick clouds, on August 12,2010, the first L5 trojan,2008 LC18, was announced. It was discovered by a survey that scanned regions where the light from the stars near the Galactic Center is obscured by dust clouds. This suggests that large L5 trojans are as common as large L4 trojans, to within uncertainty and it would have been possible for the New Horizons spacecraft to investigate L5 Neptune trojans discovered by 2014, when it passed through this region of space en route to Pluto. Some of the patches where the light from the Galactic Center is obscured by dust clouds are along New Horizonss flight path, allowing detection of objects that the spacecraft could image. 2011 HM102, the highest-inclination Neptune trojan known, was just bright enough for New Horizons to observe it in end-2013 at a distance of 1.2 AU. However, New Horizons may not have had sufficient downlink bandwidth, the orbits of Neptune trojans are highly stable, Neptune may have retained up to 50% of the original post-migration trojan population over the age of the Solar System. Neptunes L5 can host stable trojans equally well as its L4, Neptune trojans can librate up to 30° from their associated Lagrangian points with a 10, 000-year period. Neptune trojans that escape enter orbits similar to centaurs, although Neptune cannot currently capture stable trojans, roughly 2. 8% of the centaurs within 34 AU are predicted to be Neptune co-orbitals. Of these, 54% would be in horseshoe orbits, 10% would be quasi-satellites, the unexpected high-inclination trojans are the key to understanding the origin and evolution of the population as a whole. The existence of high-inclination Neptune trojans points to a capture during planetary migration instead of in situ or collisional formation. The estimated equal number of large L5 and L4 trojans indicates that there was no gas drag during capture, the capture of Neptune trojans during a migration of the planets occurs via process similar to the chaotic capture of Jupiter trojans in the Nice model. When Uranus and Neptune are near but not in a mean-motion resonance the period at which the locations where Uranus passes Neptune circulate can resonate with the periods of Neptune trojans

33.
Neptune
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Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the planet. Neptune is 17 times the mass of Earth and is more massive than its near-twin Uranus. Neptune orbits the Sun once every 164.8 years at a distance of 30.1 astronomical units. It is named after the Roman god of the sea and has the astronomical symbol ♆, Neptune is not visible to the unaided eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to perturbation by an unknown planet. Neptune was subsequently observed with a telescope on 23 September 1846 by Johann Galle within a degree of the predicted by Urbain Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the remaining known 14 moons were located telescopically until the 20th century. The planets distance from Earth gives it a small apparent size. Neptune was visited by Voyager 2, when it flew by the planet on 25 August 1989, the advent of the Hubble Space Telescope and large ground-based telescopes with adaptive optics has recently allowed for additional detailed observations from afar. Neptunes composition can be compared and contrasted with the Solar Systems other giant planets, however, its interior, like that of Uranus, is primarily composed of ices and rock, which is why Uranus and Neptune are normally considered ice giants to emphasise this distinction. Traces of methane in the outermost regions in part account for the blue appearance. In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptunes atmosphere has active, for example, at the time of the Voyager 2 flyby in 1989, the planets southern hemisphere had a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, because of its great distance from the Sun, Neptunes outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching 55 K. Temperatures at the centre are approximately 5,400 K. Neptune has a faint and fragmented ring system. On both occasions, Galileo seems to have mistaken Neptune for a star when it appeared close—in conjunction—to Jupiter in the night sky, hence. At his first observation in December 1612, Neptune was almost stationary in the sky because it had just turned retrograde that day and this apparent backward motion is created when Earths orbit takes it past an outer planet. Because Neptune was only beginning its yearly cycle, the motion of the planet was far too slight to be detected with Galileos small telescope

34.
Astronomical unit
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The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation

35.
Classical Kuiper belt object
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A classical Kuiper belt object, also called a cubewano, is a low-eccentricity Kuiper belt object that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major axes in the 40–50 AU range and, unlike Pluto and that is, they have low-eccentricity and sometimes low-inclination orbits like the classical planets. The name cubewano derives from the first trans-Neptunian object found after Pluto, similar objects found later were often called QB1-os, or cubewanos, after this object, though the term classical is much more frequently used in the scientific literature. Most cubewanos are found between the 2,3 orbital resonance with Neptune and the 1,2 resonance,50000 Quaoar, for example, has a near-circular orbit close to the ecliptic. Plutinos, on the hand, have more eccentric orbits bringing some of them closer to the Sun than Neptune. The majority of objects, have low inclinations and near-circular orbits, a smaller population is characterised by highly inclined, more eccentric orbits. The Deep Ecliptic Survey reports the distributions of the two populations, one with the inclination centered at 4. 6° and another with inclinations extending beyond 30°, the vast majority of KBOs have inclinations of less than 5° and eccentricities of less than 0.1. The hot and cold populations are different, more than 30% of all cubewanos are in low inclination. The parameters of the orbits are more evenly distributed, with a local maximum in moderate eccentricities in 0. 15–0.2 range. See also the comparison with scattered disk objects, when orbital inclinations are compared, hot cubewanos can be easily distinguished by their higher inclinations, as the plutinos typically keep orbits below 20°. In addition to the orbital characteristics, the two populations display different physical characteristics. The difference in colour between the red cold population and more heterogeneous hot population was observed as early as in 2002, another difference between the low-inclination and high-inclination classical objects is the observed number of binary objects. Binaries are quite common on low-inclination orbits and are typically similar-brightness systems, binaries are less common on high-inclination orbits and their components typically differ in brightness. There is no definition of cubewano or classical KBO. However, the terms are used to refer to objects free from significant perturbation from Neptune. The Minor Planet Center and the Deep Ecliptic Survey do not list cubewanos using the same criteria, many TNOs classified as cubewanos by the MPC are classified as ScatNear by the DES. Dwarf planet Makemake is such a borderline classical cubewano/scatnear object,2002 KX14 may be an inner cubewano near the plutinos. Furthermore, there is evidence that the Kuiper belt has an edge, in that an apparent lack of objects beyond 47–49 AU was suspected as early as 1998

36.
Makemake
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Makemake is a dwarf planet and perhaps the largest Kuiper belt object in the classical population, with a diameter approximately two thirds that of Pluto. Makemake has one satellite, S/20151. Makemake’s extremely low temperature, about 30 K, means its surface is covered with methane, ethane. Makemake was discovered on March 31,2005, by a led by Michael E. Brown. Initially, it was known as 2005 FY9 and later given the minor-planet number 136472, Makemake was recognized as a dwarf planet by the International Astronomical Union in July 2008. Its name derives from Makemake in the mythology of the Rapa Nui people of Easter Island. Makemake was discovered on March 31,2005, by a team at the Palomar Observatory, led by Michael E. Brown, despite its relative brightness, Makemake was not discovered until well after many much fainter Kuiper belt objects. Most searches for minor planets are conducted relatively close to the ecliptic, besides Pluto, Makemake is the only other dwarf planet that was bright enough that Clyde Tombaugh could have detected it during his search for trans-Neptunian planets around 1930. At the time of Tombaughs survey, Makemake was only a few degrees from the ecliptic, near the border of Taurus and Auriga, at an apparent magnitude of 16.0. This position, however, was very near the Milky Way. Tombaugh continued searching for years after the discovery of Pluto. The provisional designation 2005 FY9 was given to Makemake when the discovery was made public, before that, the discovery team used the codename Easterbunny for the object, because of its discovery shortly after Easter. In July 2008, in accordance with IAU rules for classical Kuiper belt objects,2005 FY9 was given the name of a creator deity. The name of Makemake, the creator of humanity and god of fertility in the myths of the Rapa Nui, as of December 2015, Makemake is 52.4 AU from the Sun, almost as far from the Sun as it ever reaches on its orbit. Makemake follows a very similar to that of Haumea, highly inclined at 29°. Nevertheless, Makemakes orbit is farther from the Sun in terms of both the semi-major axis and perihelion. Its orbital period is nearly 310 years, more than Plutos 248 years, both Makemake and Haumea are currently far from the ecliptic—the angular distance is almost 29°. Makemake is approaching its 2033 aphelion, whereas Haumea passed its aphelion in early 1992, Makemake is a classical Kuiper belt object, which means its orbit lies far enough from Neptune to remain stable over the age of the Solar System

37.
Resonant trans-Neptunian object
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In astronomy, a resonant trans-Neptunian object is a trans-Neptunian object in mean-motion orbital resonance with Neptune. The orbital periods of the resonant objects are in a simple integer relations with the period of Neptune e. g.1,2,2,3 etc, resonant TNOs can be either part of the main Kuiper belt population, or the more distant scattered disc population. The diagram illustrates the distribution of the known trans-Neptunian objects, resonant objects are plotted in red. The designation 2,3 or 3,2 both refer to the resonance for TNOs. There is no ambiguity, because TNOs have, by definition, the usage depends on the author and the field of research. Detailed analytical and numerical studies of Neptune’s resonances have shown that the objects must have a precise range of energies. If the objects semi-major axis is outside these ranges, the orbit becomes chaotic. As TNOs were discovered, more than 10% were found to be in 2,3 resonances and it is now believed that the objects have been collected from wider distances by sweeping resonances during the migration of Neptune. During this relatively short period of time, Neptunes resonances would be sweeping the space, the 2,3 resonance at 39.4 AU is by far the dominant category among the resonant objects, with 92 confirmed and 104 possible member bodies. The objects following orbits in this resonance are named plutinos after Pluto, the objects are rather small and most of them follow orbits close to the ecliptic. Twotinos have inclinations less than 15 degrees and generally moderate eccentricities, there are far fewer objects in this resonance than plutinos. Consequently, it might be that twotinos were originally as numerous as plutinos and these Neptune trojans, termed by analogy to the Trojan asteroids, are in 1,1 resonance with Neptune. One of the concerns is that weak resonances may exist and would be difficult to due to the current lack of accuracy in the orbits of these distant objects. Many objects have orbital periods of more than 300 years and most have only observed over a short observation arc of a couple years. A true resonance will smoothly oscillate while a coincidental near resonance will circulate, simulations by Emel’yanenko and Kiseleva in 2007 show that 2001 XT254 is librating in a 3,7 resonance with Neptune. This libration can be stable for less than 100 million to billions of years, Emel’yanenko and Kiseleva also show that 1995 TL8 appears to have less than a 1% probability of being in a 3,7 resonance with Neptune, but it does execute circulations near this resonance. The classes of TNO have no universally agreed definitions, the boundaries are often unclear. The Deep Ecliptic Survey introduced formally defined dynamical classes based on long-term forward integration of orbits under the combined perturbations from all four giant planets

38.
Plutino
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In astronomy, a plutino is a trans-Neptunian object in 2,3 mean-motion resonance with Neptune. For every 2 orbits that a plutino makes, Neptune orbits 3 times, the term plutino derived from the dwarf planet Pluto, the largest and the first plutino discovered. The term does not imply common physical characteristics, Plutinos are named after mythological creatures associated with the underworld. Plutinos form the part of the Kuiper belt and represent about a quarter of the known Kuiper belt objects. Plutinos are the largest class of the resonant trans-Neptunian objects, aside from Pluto itself, the first plutino,1993 RO, was discovered on September 16,1993. It is thought that objects that are currently in mean orbital resonances with Neptune initially followed independent heliocentric paths. As Neptune migrated outward early in the Solar Systems history, the bodies it approached would have been scattered, during this process, the 3,2 resonance is the strongest and most stable among all resonances. This is the reason it contains the largest number of bodies. The orbital periods of plutinos cluster around 247.3 years, the gravitational influence of Pluto is usually neglected given its small mass. However, the width is very narrow and only a few times larger than Pluto’s Hill sphere. Consequently, depending on the eccentricity, some plutinos will be driven out of the resonance by interactions with Pluto. Numerical simulations suggest that the orbits of plutinos with an eccentricity 10%–30% smaller or larger than that of Pluto are not stable over Ga timescales, the plutinos brighter than HV=6 include, David Jewitt on Plutinos Minor Planet Center, List of TNOs MPC List of Distant Minor Planets

39.
Pluto
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Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered, Pluto was discovered by Clyde Tombaugh in 1930 and was originally considered to be the ninth planet from the Sun. After 1992, its planethood was questioned following the discovery of objects of similar size in the Kuiper belt. In 2005, Eris, which is 27% more massive than Pluto, was discovered and this led the International Astronomical Union to define the term planet formally in 2006, during their 26th General Assembly. That definition excluded Pluto and reclassified it as a dwarf planet, Pluto is the largest and second-most-massive known dwarf planet in the Solar System and the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris, like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small—about one-sixth the mass of the Moon and one-third its volume. It has an eccentric and inclined orbit during which it ranges from 30 to 49 astronomical units or AU from the Sun. This means that Pluto periodically comes closer to the Sun than Neptune, light from the Sun takes about 5.5 hours to reach Pluto at its average distance. Pluto has five moons, Charon, Styx, Nix, Kerberos. Pluto and Charon are sometimes considered a system because the barycenter of their orbits does not lie within either body. The IAU has not formalized a definition for binary dwarf planets, on July 14,2015, the New Horizons spacecraft became the first spacecraft to fly by Pluto. During its brief flyby, New Horizons made detailed measurements and observations of Pluto, on October 25,2016, at 05,48 pm ET, the last bit of data was received from New Horizons from its close encounter with Pluto on July 14,2015. In the 1840s, Urbain Le Verrier used Newtonian mechanics to predict the position of the then-undiscovered planet Neptune after analysing perturbations in the orbit of Uranus. Subsequent observations of Neptune in the late 19th century led astronomers to speculate that Uranuss orbit was being disturbed by another planet besides Neptune, by 1909, Lowell and William H. Pickering had suggested several possible celestial coordinates for such a planet. Lowell and his observatory conducted his search until his death in 1916, unknown to Lowell, his surveys had captured two faint images of Pluto on March 19 and April 7,1915, but they were not recognized for what they were. There are fourteen other known prediscovery observations, with the oldest made by the Yerkes Observatory on August 20,1909. Percivals widow, Constance Lowell, entered into a legal battle with the Lowell Observatory over her late husbands legacy. Tombaughs task was to image the night sky in pairs of photographs, then examine each pair

40.
Scattered disc
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The scattered disc is a distant circumstellar disc in the Solar System that is sparsely populated by icy minor planets, a subset of the broader family of trans-Neptunian objects. The scattered-disc objects have orbital eccentricities ranging as high as 0.8, inclinations as high as 40° and these extreme orbits are thought to be the result of gravitational scattering by the gas giants, and the objects continue to be subject to perturbation by the planet Neptune. Although the closest scattered-disc objects approach the Sun at about 30–35 AU and this makes scattered objects among the most distant and coldest objects in the Solar System. Eventually, perturbations from the giant planets send such objects towards the Sun, many Oort cloud objects are also thought to have originated in the scattered disc. Detached objects are not sharply distinct from scattered disc objects, during the 1980s, the use of CCD-based cameras in telescopes made it possible to directly produce electronic images that could then be readily digitized and transferred to digital images. Because the CCD captured more light than film and the blinking could now be done at a computer screen. A flood of new discoveries was the result, over a thousand objects were detected between 1992 and 2006. The first scattered-disc object to be recognised as such was 1996 TL66, three more were identified by the same survey in 1999,1999 CV118,1999 CY118, and 1999 CF119. The first object presently classified as an SDO to be discovered was 1995 TL8, as of 2011, over 200 SDOs have been identified, including 2007 UK126,2002 TC302, Eris, Sedna and 2004 VN112. Known trans-Neptunian objects are divided into two subpopulations, the Kuiper belt and the scattered disc. A third reservoir of trans-Neptunian objects, the Oort cloud, has been hypothesized, some researchers further suggest a transitional space between the scattered disc and the inner Oort cloud, populated with detached objects. Those in 3,2 resonances are known as plutinos, because Pluto is the largest member of their group, in contrast to the Kuiper belt, the scattered-disc population can be disturbed by Neptune. Scattered-disc objects come within range of Neptune at their closest approaches. Some objects, like 1999 TD10, blur the distinction and the Minor Planet Center, the MPC also makes a clear distinction between the Kuiper belt and the scattered disc, separating those objects in stable orbits from those in scattered orbits. Another term used is scattered Kuiper-belt object for bodies of the scattered disc and this delineation is inadequate over the age of the Solar System, since bodies trapped in resonances could pass from a scattering phase to a non-scattering phase numerous times. That is, trans-Neptunian objects could travel back and forth between the Kuiper belt and the disc over time. In the a >30 AU region, the region of the Solar System populated by objects with semi-major axes greater than 30 AU, the Minor Planet Center classifies the trans-Neptunian object 90377 Sedna as a scattered-disc object. Under this definition, an object with a greater than 40 AU could be classified as outside the scattered disc

41.
Eris (dwarf planet)
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Eris is the most massive and second-largest dwarf planet known in the Solar System. It is also the known body directly orbiting the Sun. It is measured to be 2,326 ±12 kilometers in diameter, Eris is 27% more massive than dwarf planet Pluto, though Pluto is slightly larger by volume. Eris mass is about 0. 27% of the Earths mass, Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its identity was verified later that year. It is an object and a member of a high-eccentricity population known as the scattered disk. It has one moon, Dysnomia. As of February 2016, its distance from the Sun is 96.3 astronomical units, because Eris appeared to be larger than Pluto, NASA initially described it as the Solar Systems tenth planet. This, along with the prospect of other objects of similar size being discovered in the future, motivated the International Astronomical Union to define the term planet for the first time. Observations of an occultation by Eris in 2010 showed that its diameter was 2,326 ±12 kilometers, very slightly less than Pluto. Eris was discovered by the team of Mike Brown, Chad Trujillo, the discovery was announced on July 29,2005, the same day as Makemake and two days after Haumea, due in part to events that would later lead to controversy about Haumea. Routine observations were taken by the team on October 21,2003, in January 2005, the re-analysis revealed Eriss slow motion against the background stars. Follow-up observations were carried out to make a preliminary determination of Eriss orbit. More observations released in October 2005 revealed that Eris has a moon, observations of Dysnomias orbit permitted scientists to determine the mass of Eris, which in June 2007 they calculated to be ×1022 kg, 27%±2% greater than Plutos. Eris is named after the Greek goddess Eris, a personification of strife, the regular adjectival form of Eris is Eridian. As a result, for a time the object known to the wider public as Xena. Xena was a name used internally by the discovery team. It was inspired by the character of the television series Xena. The discovery team had saved the nickname Xena for the first body they discovered that was larger than Pluto

42.
Perihelion and aphelion
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The perihelion is the point in the orbit of a celestial body where it is nearest to its orbital focus, generally a star. It is the opposite of aphelion, which is the point in the orbit where the body is farthest from its focus. The word perihelion stems from the Ancient Greek words peri, meaning around or surrounding, aphelion derives from the preposition apo, meaning away, off, apart. According to Keplers first law of motion, all planets, comets. Hence, a body has a closest and a farthest point from its parent object, that is, a perihelion. Each extreme is known as an apsis, orbital eccentricity measures the flatness of the orbit. Because of the distance at aphelion, only 93. 55% of the solar radiation from the Sun falls on a given area of land as does at perihelion. However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earths axis, which is 23.4 degrees away from perpendicular to the plane of Earths orbit around the sun. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, in the northern hemisphere, summer occurs at the same time as aphelion. Despite this, there are larger land masses in the northern hemisphere, consequently, summers are 2.3 °C warmer in the northern hemisphere than in the southern hemisphere under similar conditions. Apsis Ellipse Solstice Dates and times of Earths perihelion and aphelion, 2000–2025 from the United States Naval Observatory

43.
Detached object
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Detached objects are a dynamical class of minor planets in the outer reaches of the Solar System and belong to the broader family of trans-Neptunian objects. This reflects the dynamical gradation that can exist between the parameters of the scattered disk and the detached population. At least nine such bodies have been identified, of which the largest, most distant. Those with perihelia greater than 75 AU are termed sednoids, as of 2016, there are two known sednoids, Sedna and 2012 VP113. Detached objects have much larger than Neptunes aphelion. They often have highly elliptical, very large orbits with semi-major axes of up to a few hundred astronomical units, such orbits cannot have been created by gravitational scattering by the giant planets. Instead, a number of explanations have been put forward, including an encounter with a star or a distant planet-sized object. The classification suggested by the Deep Ecliptic Survey team introduces a distinction between scattered-near objects and scattered-extended objects using a Tisserands parameter value of 3. Detached objects are one of five distinct classes of TNO, the other four classes are classical Kuiper-belt objects, resonant objects, scattered-disc objects. Detached objects generally have a distance greater than 40 AU, deterring strong interactions with Neptune. However, there are no boundaries between the scattered and detached regions, since both can coexist as TNOs in an intermediate region with perihelion distance between 37 and 40 AU. One such intermediate body with a well determined orbit is 2003 FY128, although Sedna is officially considered a scattered-disc object by the MPC, its discoverer Michael E. This classification of Sedna as an object is accepted in recent publications. They have orbital periods of more than 300 years and most have only observed over a short observation arc of a couple years. Further improvement in the orbit and potential resonance of objects will help to understand the migration of the giant planets. For example, simulations by Emel’yanenko and Kiseleva in 2007 show that many distant objects could be in resonance with Neptune. They show a 10% likelihood that 2000 CR105 is in a 20,1 resonance, a 38% likelihood that 2003 QK91 is in a 10,3 resonance, and an 84% likelihood that 2000 YW134 is in an 8,3 resonance. The likely dwarf planet 2005 TB190 appears to have less than a 1% likelihood of being in a 4,1 resonance

44.
90377 Sedna
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90377 Sedna is a large minor planet in the outer reaches of the Solar System that was, as of 2015, at a distance of about 86 astronomical units from the Sun, about three times as far as Neptune. Spectroscopy has revealed that Sednas surface composition is similar to that of some other objects, being largely a mixture of water, methane. Its surface is one of the reddest among Solar System objects and it is most likely a dwarf planet. Sedna has a long and elongated orbit, taking approximately 11,400 years to complete. These facts have led to speculation about its origin. The Minor Planet Center currently places Sedna in the scattered disc, others speculate that it might have been tugged into its current orbit by a passing star, perhaps one within the Suns birth cluster, or even that it was captured from another star system. Another hypothesis suggests that its orbit may be evidence for a planet beyond the orbit of Neptune. Astronomer Michael E. Sedna was discovered by Michael Brown, Chad Trujillo, the discovery formed part of a survey begun in 2001 with the Samuel Oschin telescope at Palomar Observatory near San Diego, California using Yales 160 megapixel Palomar Quest camera. On that day, an object was observed to move by 4.6 arcseconds over 3.1 hours relative to stars, later, the object was precovered on older images made by the Samuel Oschin telescope as well as on images from the Near-Earth Asteroid Tracking consortium. These previous positions expanded its known orbital arc and allowed a precise calculation of its orbit. The team made the name Sedna public before the object had been officially numbered, brian Marsden, the head of the Minor Planet Center, said that such an action was a violation of protocol, and that some members of the IAU might vote against it. However, no objection was raised to the name, and no competing names were suggested, Sedna has the longest orbital period of any known object in the Solar System of comparable size or larger, calculated at around 11,400 years. Its orbit is eccentric, with an aphelion estimated at 937 AU. This perihelion was the largest of that of any known Solar System object until the discovery of 2012 VP113, at its aphelion, Sedna orbits the Sun at a mere 4% of Earths orbital speed. When Sedna was discovered it was 89.6 AU from the Sun approaching perihelion, Eris was later detected by the same survey near aphelion at 97 AU. Only the orbits of some long-period comets extend farther than that of Sedna, when first discovered, Sedna was thought to have an unusually long rotational period. It was initially speculated that Sednas rotation was slowed by the pull of a large binary companion. Sedna has a V-band absolute magnitude of about 1.8, at the time of its discovery it was the intrinsically brightest object found in the Solar System since Pluto in 1930

An Euler diagram (OY-lər) is a diagrammatic means of representing sets and their relationships. Typically they …

Both the Veitch and Karnaugh diagrams show all the minterms, but the Veitch is not particularly useful for reduction of formulas. Observe the strong resemblance between the Venn and Karnaugh diagrams; the colors and the variables x, y, and z are per Venn's example.

Composite of two pages 115–116 from Venn 1881 showing his example of how to convert a syllogism of three parts into his type of diagram. Venn calls the circles "Eulerian circles" (cf Sandifer 2003, Venn 1881:114 etc) in the "Eulerian scheme" (Venn 1881:100) of "old-fashioned Eulerian diagrams" (Venn 1881:113).

The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, with internal …

During a total solar eclipse, the solar corona can be seen with the naked eye, during the brief period of totality.

Taken by Hinode's Solar Optical Telescope on 12 January 2007, this image of the Sun reveals the filamentary nature of the plasma connecting regions of different magnetic polarity.

Visible light photograph of sunspot, 13 December 2006

In this false-color ultraviolet image, the Sun shows a C3-class solar flare (white area on upper left), a solar tsunami (wave-like structure, upper right) and multiple filaments of plasma following a magnetic field, rising from the stellar surface.

The definition of planet set in Prague, Czech Republic, in August 2006 by the International Astronomical Union (IAU) …

The original proposal would have immediately added three planets, shown here in a size comparison to Earth. Leftmost is Pluto (shown in lieu of Eris, which is about the same size), then Charon, Ceres, and Earth

The twelve "candidate planets" that were possibilities for inclusion under the originally proposed definition. Note that all but the last three are trans-Neptunian objects. The smallest three (Vesta, Pallas, Hygeia) are in the asteroid belt.

Satirical protest demonstration against the "demotion" of Pluto

Plenary session of the IAU General Assembly on August 24, 2006. Votes were cast by raising yellow cards.

Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass …

Jupiter's diameter is one order of magnitude smaller (×0.10045) than that of the Sun, and one order of magnitude larger (×10.9733) than that of Earth. The Great Red Spot is roughly the same size as Earth.

The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars …

By far the largest object within the belt is Ceres. The total mass of the asteroid belt is significantly less than Pluto's, and approximately twice that of Pluto's moon Charon.

Johannes Kepler, who first noticed in 1596 that there was something strange about the orbits of Mars and Jupiter.

Giuseppe Piazzi, discoverer of Ceres, the largest object in the asteroid belt. For several decades after its discovery Ceres was known as a planet, after which it was reclassified as asteroid. In 2006, it was designated as a dwarf planet.

951 Gaspra, the first asteroid imaged by a spacecraft, as viewed during Galileos 1991 flyby; colors are exaggerated

Conic sections describe the possible orbits (yellow) of small objects around the Earth. A projection of these orbits onto the gravitational potential (blue) of the Earth makes it possible to determine the orbital energy at each point in space.

This image shows the four trajectory categories with the gravitational potential well of the central mass's field of potential energy shown in black and the height of the kinetic energy of the moving body shown in red extending above that, correlating to changes in speed as distance changes according to Kepler's laws.

This graphic shows the distance from the Oort cloud to the rest of the Solar System and two of the nearest stars measured in astronomical units. The scale is logarithmic, with each specified distance ten times further out than the previous one. Red arrow indicates location of Voyager 1, a space probe that will reach the Oort cloud in 300 years.

Simulation showing Outer Planets and Kuiper Belt: a) Before Jupiter/Saturn 2:1 resonance b) Scattering of Kuiper-belt objects into the Solar System after the orbital shift of Neptune c) After ejection of Kuiper-belt bodies by Jupiter

The infrared spectra of both Eris and Pluto, highlighting their common methane absorption lines

The astronomical unit (symbol: au or ua) is a unit of length, roughly the distance from Earth to the Sun. However, that …

The red line indicates the Earth–Sun distance, which on average is about 1 astronomical unit.

Transits of Venus across the face of the Sun were, for a long time, the best method of measuring the astronomical unit, despite the difficulties (here, the so-called "black drop effect") and the rarity of observations.

The astronomical unit is used as the baseline of the triangle to measure stellar parallaxes (distances in the image are not to scale).